Electrical capacitors



ELECTRICAL CAPACITORS Filed June 10, 1952 5 w m 2 /a I I. s 5 1 I, W

ATTOR/:EVS

United States Patent Q ELECTRICAL CAPACKTQRS William M. Allison,Willlamstown, Mass, assignor to Sprague Electric Company, North Adams,Mass a corporation of Massachusetts Application June 10, 1952, SerialNo. 2921,6555

1 Claim. (1. 317-259) The present invention relates to new and improvedelectrical capacitors.

More particularly, this invention relates to a. new tyne of Woundelectrostatic capacitor which overcomes the problems resulting from theso-called margin erect. With most wound capacitance units, the usualmargins diiliculty is that the electrostatic gradient is concentrated atthe edge of the electrodes. This leads to breakdown at the portion ofthe dielectric separating the foil edges.

it is an object of this invention to produce an electrostatic capacitorwhich is not subjected to this d fficulty. A further object or" theinvention is to produce a new and improved electrostatic capacitor whichwill not break down because of any electrostatic concentration withinthe capacitance foils. These and other objects of the invention will beseen in this specification and the appended claims.

The above objects are obtained by spirally Winding the various parts ofan electrostatic capacitor around a core in much the same manner as acontinuous paper strip is wound forming a common soda straw. The variousnecessary strips are applied on top of one an other until all of theelements or" an electrostatic capacitor are present. The final windingsare removed from the central core and either wound into a cylinder orstacked or bent to a desired configuration.

These new constructions of the invention are more specifically seen fromthe accompanying drawing in which Figure 1 diagrammatically shows thespiral winding of capacitance units and in which Figure 2 pictures afiat wound unit formed from a spiralled unit in accordance with theinvention. For convenience, the same numerals designate like parts inboth figures.

In forming the new capacitors of this invention, first a metallic foil12 is Wound about a central core 11 in an endless fashion. Next, adielectric sheet 13 is applied on top of this foil in the same manner ofWinding. A second electrode 14 is then applied upon the dielectric 13 inthe spiral manner, and this, in turn, is covered by a fourth winding ofa second dielectric 15. In all of these cases the direction of windingis substantially immaterial and the various layers can be applied bywinding in opposite directions.

Once the various foils and dielectrics have been positioned, the core 11is removed and the entire spiral is pressed so as to assume a flatconfiguration. It is then rolled into a capacitance unit and provisionsfor electrical connections are made in conventional manner at the end ofthe wound cylinders.

One manner of inserting terminal tabs is shown in Figure 2. Here a tab17 has been inserted within the space formerly occupied by the core 11prior to the flattening of the unit and a second electrode tab 16 isWound next to an exposed portion of the electrode foil 14. Other meanssuch as exposing both of the electrode layers employed and solderingleads directly to them can be utilized.

It is possible to modify the procedure indicated in the above discussionin several manners; instead of separate dielectric and electrode layers,metallized dielectrics in 2,735,351 li atented Mar. 12, 1957 which themetallic coating confined to only one surcoated layers being wound withthe coatings out of c htact with one another. Also, several separate odielectric or layers of diiierent dielectrics can employed between theelectrodes. A further modification of this invention is to delete-'ctric of Figure l leaving a capacitor t. g metallic foils 12 and 14separated by the dielectric i3. Arter the foils l2 and 14- anddielectric i3 are positioned upon the central core 11 the core 11 isremoved and the entire spiral is pressed so as to assume configuration.The unit is rolled into a capacitor in one electrode forms the outersegment of the The edges of the outer foil of said casaid capacitpacitor are joined, as by solderinr or metallic spraying, to providemechanical strength to the rolled unit in addition to decreasing theresidual inductance of the capacitor. A terminal tab for this outerelectrode 14 is connected to the soldered edges r it may be mechanicallyand electricall connected to the plane of the outer foil. he secondelectrode tab, connected to the inner metallic l 1.2, is brought outfrom the outer end of the spiraled it and protected from the outermetallic foil 14 by an extension of the dielectric 13 beyond the outerend of said foil ther methods of connecting the tabs are equallysuitable e. g. the tab 16 might be brought out through the center of thespiral by providing suitable insulation from outer metallic foil Thebroad of LhiS invention extend to continuous dielectric tubings. Suchtubings can be metallized on one or both surfaces and wound into asingle itance unit. it will he realized that these dielectric tee .igsdo not have to be wound into a spiral before being flattened, but canmerely flattened and then wound into a final unit.

Once the capacitance sections of this invention have been formed, theycan be impregnated with any of the impregnants normally used in the art,such as, for example chlorinated naphthalene or the like. Protectivecoatings of Wax, resin, or the like, can be applied to them, and theseunits can be encased in any of the many of the manners known to the art.

As many apparently widely diiferent embodiments of my invention may bemade without departing from the spirit and scope hereof, it is to beunderstood that my invention is not limited to the specific embodimentshereof except as defined in the appended claim.

What I claim is:

A capacitor comprising a first fiat tubular metallic electrode ofhelically wound strip enveloped by a fiat sleeve of helically wounddielectric ribbon, all the adjacent turns of said wound ribbon being inpartially overlapped relationship, and a fiat tubular metallic electrodesleeve of helically wound strip enveloping the dielectric sleeve andseparated from the first electrode, said flat assembly being rolled upin the direction of its longitudinal axis.

References Cited in the file of this patent UNITED STATES PATENTS

